U.S. patent application number 10/208038 was filed with the patent office on 2003-04-24 for method for forming a honeycomb sandwich composite panel.
Invention is credited to Maruyama, Seiji, Yamaguchi, Eikatsu.
Application Number | 20030077410 10/208038 |
Document ID | / |
Family ID | 19067896 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030077410 |
Kind Code |
A1 |
Yamaguchi, Eikatsu ; et
al. |
April 24, 2003 |
Method for forming a honeycomb sandwich composite panel
Abstract
A method for forming a honeycomb sandwich composite panel
comprising dry fabrics, an unpermeating-resin film, a
non-low-viscosity-resin film, a honeycomb core, a non-low-viscosity
resin film, an unpermeating-resin film and dry fabrics, stacked in
this order in a mold. The cells of the honeycomb core are sealed by
the laminated films. The unpermeating-resin film prevents the
excessive permeation of the resin which forms the laminated films
into the dry fabrics and to enhance the adhesion of this resin to
the honeycomb core by forming proper fillets of the resin of the
laminated sealing films. Further, drying process for drying the dry
fabrics enables the application of the RTM process to the formation
of the honeycomb sandwich composite panel.
Inventors: |
Yamaguchi, Eikatsu;
(Tokyo-To, JP) ; Maruyama, Seiji; (Tokyo-To,
JP) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
19067896 |
Appl. No.: |
10/208038 |
Filed: |
August 1, 2002 |
Current U.S.
Class: |
428/36.2 ;
156/197; 156/245; 428/36.91 |
Current CPC
Class: |
B29C 70/088 20130101;
Y10T 428/1393 20150115; Y10T 156/1003 20150115; B32B 27/40
20130101; B32B 27/38 20130101; B32B 3/12 20130101; B32B 2398/10
20130101; Y10T 428/24157 20150115; Y10T 428/1366 20150115; B32B
27/08 20130101; B32B 37/146 20130101; B32B 2250/05 20130101; B32B
2250/40 20130101; B29C 70/48 20130101; B32B 2309/025 20130101; B32B
27/12 20130101 |
Class at
Publication: |
428/36.2 ;
156/245; 428/36.91; 156/197 |
International
Class: |
B65D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2001 |
JP |
2001-236673 |
Claims
What is claimed is:
1. A method for forming a honeycomb sandwich composite panel
comprising the steps of: stacking dry fabrics, an
unpermeating-resin film, a non-low-viscosity-resin film, a
honeycomb core, a non-low-viscosity resin film, an
unpermeating-resin film and dry fabrics in this order to form a
stacked structure on a lower half mold of a mold; putting an upper
half mold of the mold on the stacked structure and clamping
together the upper half mold and the lower half mold; closing resin
supply ports and air ports formed in the upper and the lower half
mold; heating an interior of the mold at a first temperature for a
predetermined heating time to cure the unpermeating-resin films and
the non-low-viscosity-resin films and to dry the dry fabrics;
connecting the air ports of the upper and the lower half molds to
an evacuating device; connecting the resin supply ports to a resin
supply passage; closing the resin supply passage, changing a
temperature of the interior of the mold to a second temperature
while the interior of the mold is evacuated; and supplying an
impregnating resin into the mold to impregnate the dry fabrics with
the impregnating resin; and heating the interior of the mold at a
third temperature for a predetermined heating time to cure the
impregnating resin supplied into the mold.
2. The method for forming a honeycomb sandwich composite panel
according to claim 1, wherein the impregnating resin is a
thermosetting epoxy resin or a thermosetting polycyanate resin,
said unpermeating-resin film contains a thermosetting epoxy resin,
and said non-low-viscosity-resin film is formed of a thermosetting
epoxy resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a lightweight,
high-stiffness honeycomb composite panel used in aircraft,
automobiles, ships, buildings and general industrial equipment and,
more particularly, to a method for forming the honeycomb sandwich
composite panel using an RTM (resin transfer molding) process.
[0003] 2. Description of the Related Art
[0004] In a previously known method for forming a honeycomb
sandwich panel, outer panels formed as skins are placed on the top
and bottom surfaces of a honeycomb core respectively and are bonded
to the honeycomb core with an adhesive applied therebetween under
heat and pressure. In another previously known method, prepreg
sheets are stacked by hand lay-up operation on the top and bottom
surfaces of a honeycomb core respectively, and are bonded to the
honeycomb core with an adhesive applied therebetween in a vacuum
space established in a vacuum bag enclosing the prepreg sheets and
the honeycomb core using a hot press or an autoclave.
[0005] In addition, Japanese Patent Laid-Open No. 295362/1997
describes a method for forming a honeycomb sandwich panel using the
RTM process, in which an impregnating resin is prevented from
flowing into the cells of a honeycomb core with resin/moisture
barrier films formed of a particular macromolecular film.
[0006] A method for forming a honeycomb sandwich composite panel
disclosed in JP-A No. 5502968/2000 uses a polyimide film, such as
Kapton.RTM. commercially available from E. I. du Pont de Nemours
and Company, as a bonding barrier layer to prevent the resin
impregnated into sheets (prepreg sheets) from flowing into the
cells of a honeycomb core when a honeycomb sandwich composite panel
is formed.
[0007] A method for forming a honeycomb sandwich composite panel
disclosed in JP-A No. 167950/2000 comprises the steps of heating
sealing materials and dry fabrics to be boned to the surfaces of a
honeycomb core at the thermosetting temperature of the sealing
materials, impregnating the dry fabric with a thermosetting resin,
and hardening the thermosetting resin impregnated into the dry
fabrics by pressing and heating those under predetermined
conditions.
[0008] The known method for forming a honeycomb sandwich composite
panel employing the RTM process needs to prevent the resin from
flowing into the cells of the honeycomb core. Therefore, the cells
of the honeycomb core need to be sealed before thermo-setting the
honeycomb core in a mold. Thus, two steps and complicated work are
necessary before starting an impregnating process, which is an
impediment of cost reduction.
[0009] The method for forming a honeycomb sandwich composite panel
disclosed in JP-A Nos. 2995362/1997 and 502968/2000 bond the skins
and the honeycomb core together with a resin/moisture-resistant
film of a specific polymer and a bonding barrier layer,
respectively. Therefore, both the surfaces of the
resin/moisture-resistant film and the bonding barrier layer must be
coated with an adhesive, which increases the weight of the
honeycomb sandwich composite panel. Generally, the specific polymer
film is unsatisfactory in adhesive property and incapable of
exerting high adhesive strength. Therefore, the film needs to be
treated beforehand by a special pretreatment process, which
increases processes and provides an impediment to cost
reduction.
[0010] Although the method for forming the honeycomb sandwich
composite panel disclosed in JP-A No. 167950/2000 is capable of
solving the aforementioned problems, this method needs at least two
thermo-setting adhesive films and epoxy resin films on the opposite
sides of a carrier member, that is this method needs many sealing
films.
SUMMARY OF THE INVENTION
[0011] The present invention has been made in view of the
aforementioned problems, and it is therefore an object of the
present invention to provide a method for forming a honeycomb
sandwich composite panel capable of forming a reliable sealing
layer consisting of a small number of component layers, and of
preventing a resin from flowing into the cells of a honeycomb core
during an impregnation process and of using a RTM process.
[0012] According to one aspect of the present invention, a method
for forming a honeycomb sandwich composite panel includes the steps
of: stacking dry fabrics, an unpermeating-resin film, a
non-low-viscosity-resin film, a honeycomb core, a non-low-viscosity
resin film, an unpermeating-resin film and dry fabrics in this
order to form a stacked structure on a lower half mold of a mold;
putting an upper half mold of the mold on the stacked structure;
clamping together the upper and the lower half mold; closing resin
supply ports and air ports formed in the upper and the lower half
mold; heating an interior of the mold at a first temperature for a
predetermined heating time to cure the unpermeating-resin films and
the non-low-viscosity-resin films and to dry the dry fabrics;
connecting the air ports of the upper and the lower half mold to an
evacuating device; connecting the resin supply ports to a resin
supply passage; closing the resin supply passage, and changing a
temperature of the interior of the mold to a second temperature
while the interior of the mold is evacuated; and supplying an
impregnating resin into the mold to impregnate the dry fabrics with
the impregnating resin and heating the interior of the mold at a
third temperature for a predetermined heating time to cure the
impregnating resin supplied into the mold.
[0013] Thus, the honeycomb sandwich composite panel forming method
is capable of preventing the impregnating resin from flowing into
the cells of the honeycomb core and of forming a honeycomb sandwich
composite panel of a satisfactory quality at a low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other objects, features and advantages of the
present invention will become more apparent from the following
description taken in connection with the accompanying drawings, in
which:
[0015] FIG. 1 is an exploded perspective view of a honeycomb
sandwich composite panel formed by the method for forming a
honeycomb sandwich composite panel of the present invention;
[0016] FIG. 2 is a fragmentary sectional view of a honeycomb
sandwich composite panel formed by the method for forming a
honeycomb sandwich composite panel of the present invention;
[0017] FIG. 3 is a diagram showing the steps of a method for
forming a honeycomb sandwich composite panel of the present
invention; and
[0018] FIG. 4 is a diagram showing the steps of second embodiment
of the method for forming a honeycomb sandwich composite panel of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Referring now to FIG. 1, a honeycomb sandwich composite
panel 1 formed by a method for forming a honeycomb sandwich
composite panel in a first embodiment according to the present
invention includes a honeycomb core 2, non-low-viscosity-resin
films 3 extended on the opposite surfaces of the honeycomb core 2
respectively, unpermeating-resin films 4 extended on the outer
surfaces of the non-low-viscosity-resin films 3 respectively, a
plurality of dry fabrics 5 stacked on the outer surface of each of
the non-low-viscosity-resin films 4. The non-low-viscosity-resin
films 3 and the unpermeating-resin films 4 are constructing sealing
members.
[0020] The non-low-viscosity-resin films 3 are such resin films
that soften when it is heated up to the curing temperature, but do
not melt and drip into the cells of the honeycomb core 2 before it
is cured, and permit small parts thereof flow along the walls
defining the cells of the honeycomb core 2 to form fillets. Resin
films suitable for use as the non-low-viscosity-resin films 3 are
selected on the basis of test results conducted on a honeycomb core
include heating the resin film up to its curing temperature and
evaluating the behavior of the resin film during heating up to the
curing temperature. Examples of resin films suitable for use as the
non-low-viscosity-resin films 3 are MB1515 curable at temperatures
in the range of 145 to 180.degree. C. and commercially available
from CYTEC Fiberite Inc, FM123-5 curable at temperatures in the
range of 115 to 155.degree. C. and commercially available from
CYTEC Industries and AF126 and AF126-2 commercially available from
Minnesota Mining and Manufacturing Co.
[0021] The unpermeating-resin films 4 are such resin films that are
cured without permeating into the dry fabrics 5 while the same are
heated up to the curing temperature. The unpermeating-resin films 5
having such a property can be prepared by mixing a proper additive
in a resin. A resin film suitable for use as the unpermeating-resin
films 4 is formed, for example, by adding glass microballoons in a
resin in a resin film forming process. A resin film AF325
commercially available from Minnesota Mining and Manufacturing Co.
is an example of such a resin film. The inventors of the present
invention found that resin films containing glass fibers or
nonwoven glass fabrics instead of glass microballoons are suitable
for use as the unpermeating-resin films 4. Thus, the
non-low-viscosity-resin film 3 and the unpermeating-resin film 4
form a laminated sealing member capable of suppressing the
permeation of the resin into the dry fabrics 5 and of surely
forming a film and fillets when heated for curing.
[0022] The dry fabrics 5 are impregnated with a thermosetting epoxy
resin or a thermosetting polycyanate resin. The honeycomb core 2
and the dry fabrics 5 are the same as those used for forming
conventional honeycomb sandwich composite panels.
[0023] The method for forming a honeycomb sandwich composite panel
embodying the present invention is now described with reference to
FIGS. 3 and 4.
[0024] Referring to FIGS. 3 and 4, the dry fabrics 5 are stacked on
a lower half mold of a mold (not shown), the unpermeating-resin
film 4 is placed on the dry fabrics 5, the non-low-viscosity-resin
film 3 is placed on the unpermeating-resin film 4, the honeycomb
core 2 is placed on the non-low-viscosity-resin film 3, the
non-low-viscosity resin film 3 is placed on the honeycomb core 2,
the unpermeating-resin film 4 is placed on the
non-low-viscosity-resin film 3, and the dry fabrics 5 are stacked
on the non-low-viscosity resin film 4 to form a stacked structure
on the lower half mold.
[0025] An upper half mold of the mold (nor shown) is put on the
stacked structure and the upper and the lower half mold are clamped
together by a mold clamping mechanism. Then, air discharge ports
and resin supply ports formed in the upper and the lower half mold
are closed by port-closing devices.
[0026] Then, the upper and the lower half mold and the stacked
structure consists of the component members are heated as shown in
FIGS. 3 or 4, to impregnate the dry fabrics 5 with an impregnating
resin, and to cure the laminated sealing films.
[0027] First, the stacked structure is heated up to a first
temperature for curing the laminated sealing films 3, 4 at a
heating rate of 1.degree. C./min, and the stacked structure is kept
at the first temperature for a predetermined time to cure the
laminated sealing films 3, 4 and to dry the dry fabrics 5.
[0028] Since the mold is sealed before starting the heating
process, there is no pressure difference between a space on the
inner side of the laminated sealing film, i.e., the interior of the
cells, and a space accommodating the dry fabrics 5, and hence
creation of defects, such as pores in the laminated sealing films
3, 4 can be avoided.
[0029] Since each laminated sealing member consists of
thermosetting epoxy resin films each having different flowing
profiles, namely, the unpermeating-resin film 4 contiguous with the
dry fabric 5 and the non-low-viscosity-resin film 3 contiguous with
the honeycomb core 2, the excessive permeation of the resin forming
the unpermeating-resin film 4 into the dry fabrics 5 can be avoided
and proper fillets capable of ensuring bonding strength can be
formed. The dry fabrics 5 are dried and each of the
non-low-viscosity-resin film 3 and the unpermeating-resin film 4
are cured to seal the cells of the honeycomb core 2 by the
foregoing steps.
[0030] Subsequently, the port-closing devices are removed to open
the air discharge ports and the resin supply ports of the upper and
the lower half mold, the opened air discharge ports are connected
to an vacuum pressure devices for evacuating the interior of the
mold, the opened resin supply ports are connected to a resin supply
line, and then the resin supply passage is closed.
[0031] Then, the interior of the mold is heated or cooled to a
second temperature for impregnating the dry fabrics 5 with an
impregnating resin, while the interior of the mold is being
evacuated. After the interior temperature of the mold has coincided
with the second temperature, the resin supply passage connected to
the resin supply ports is opened to inject the impregnating resin
into the mold at an injection pressure in the range of 0.2 to 0.3
MPa. Consequently, the dry fabrics 5 are impregnated with the
impregnating resin. After the impregnating resin starts to overflow
through the air discharge port formed in the upper half mold, the
air discharge port is closed. The resin supply line is inspected
for the leakage of the resin after the laminated sealing films have
been cured to suppress the formation of bubbles in the laminated
sealing films.
[0032] Then, the impregnating resin supplied into the mold is
heated at a third temperature higher than the second temperature
for a predetermined time to cure the impregnating resin. Thus, the
honeycomb sandwich composite panel 1 is formed.
[0033] In the honeycomb sandwich composite panel forming method
shown in FIG. 4, the second temperature is lower than the first
temperature. The first and the second temperature are dependent on
the curing temperature of the laminated sealing films and the
temperature of the impregnating resin impregnated into the dry
fabrics 5. A honeycomb sandwich composite panel having a necessary
strength and a satisfactory quality can be formed by either the
honeycomb sandwich composite panel forming method shown in FIG. 3
or the honeycomb sandwich composite panel forming method shown in
FIG. 4. The first and the second temperature are selectively
determined for further cost reduction and further improvement of
quality.
[0034] Laminated sealing films, impregnating resins, and first,
second and third temperatures for those laminated sealing films and
the resins are tabulated in Table 1.
1TABLE 1 First temperature Sealing film #1: 45 to 180.degree. C.
MB1515 and AF325 Sealing film #2: 115 to 155.degree. C. One of
FM123-2, FM123-5, AF126 and AF126-2, and AF325 Second temperature
160 .+-. 5.degree. C. 55 .+-. 5.degree. C. 55 .+-. 5.degree. C. 60
.+-. 10.degree. C. Third temperature 180 .+-. 5.degree. C. 80 to
110 .degree. C. 120 .+-. 5.degree. C. 180 .+-. 5.degree. C. RTM
resin Epoxy resin A Epoxy resin B Epoxy resin C Polycyanate resin D
Note: A: PR-500 (Minnesota Mining and Manufacturing Co.) B: TR-A31
(Toray Industries Inc.) C: YER-017, YER-058 (The Yokohama Rubber
Co., Ltd.) D: NM20 (Nippon Oil Corp.)
[0035] It goes without saying that the laminated sealing films and
the impregnating resins may be other than those shown in Table
1.
[0036] As apparent from the foregoing description, according to the
present invention, the cells of the honeycomb core are sealed by
the laminated sealing films each consisting of two films
respectively formed of different resins respectively having
different flowling profile to prevent the excessive permeation of
the resin forming the laminated sealing films into the dry fabrics
and to enhance the adhesion of the resin of the laminated sealing
films to the honeycomb core by forming proper fillets of the resin
of the laminated sealing films, drying of the dry fabrics enables
the application of the RTM process to the formation of the
honeycomb sandwich composite panel. Thus, the honeycomb sandwich
composite panel having a satisfactory quality can be fabricated at
a low cost.
[0037] Although the invention has been described in its preferred
embodiments with a certain degree of particularity, obviously many
changes and variations are possible therein. It is therefore to be
understood that the present invention may be practiced otherwise
than as specifically described herein without departing from the
scope and spirit thereof.
[0038] This application is based on the Japanese Patent Application
No. 236673/2001 filed on Aug. 3, 2001, the content of which is
herein incorporated by reference.
* * * * *